It is the object of the invention to provide a drill device with a drilling bush that is can be used independent of the shape of the workpiece so that different workpieces and different borings can be produced using the same drilling bush.
The object is solved according to the invention. Accordingly, the drilling bush is not adapted to the workpiece, but comprises a substantially straight supporting edge by which it is supported on the convex surface of the workpiece. Thus, a full-surface and sealing support at the boring edge is consciously omitted and it is accepted that drilling liquid can escape laterally at the place of contact between drilling bush and workpiece. By the substantially straight supporting edge it is achieved that the drilling bush always contacts the surface of the workpiece with the supporting edge, even when the boring is produced laterally of the apex. Thus it is avoided that two curvatures or inclined surfaces of the workpiece and the drilling bush are pressed against each other which would slide on each other and slip off due to their inclined surfaces. Preferably, the device is used to produce borings in cylindrical surfaces. Then, the supporting edge extends obliquely or rectangularly to the longitudinal axis of the workpiece and rests on the apex line of the workpiece. There is no risk of slipping off. The apex is that point of the sectional plane of the tube that, in parallel to the drilling bush axis, projects furthest towards the axis drilling bush.
Usually, drilling bushes include a wear resistant bush at the front end. Typically, the bush projects slightly so that it forms the part that should be adapted to the surface of the workpiece. The wear resistant bush is made of wear resistant steel or hard metal. In the device of the present invention, the bush need not project beyond the drilling bush but may be sunk completely in the drilling bush. Further, the wear resistant bush need not be adapted to the workpiece. The functionality of the bush is reduced to guiding the drill bit. The bush has no sealing function.
The invention allows for the use of a single drilling bush for different angles and different workpiece surfaces.
According to a preferred development of the invention, the supporting edge is delimited by a planar side surface of the drilling bush. The planar side surface facilitates the provision of a straight supporting edge at the front end.
The end of the drilling bush facing the workpiece may be designed in part as a planar front face or in part as a receding inclined surface, the supporting edge defining the planar front face. The receding inclined surface increases the opening for the escape of the outflowing drilling liquid. Due to the fact that the drilling liquid escapes into the environment before reaching the drilling bush, the chips in the drilling liquid do not enter the drilling bush and also cause no wear in the same. This prolongs the service life of the drilling bush.
Suitably, two parallel supporting edges are provided extending on either side of the longitudinal bore of the drilling bush. Thus, the drilling bush may selectively be inclined to the right or the left and otherwise maintain its orientation.
Preferably, the supporting edge is rounded or beveled. A substantially point-shaped contact between the drilling bush and the surface of the workpiece is obtained. This contact is sufficient for a stable guiding and security against displacement, in particular due to the fact that the point of contact lies on the apex of the workpiece and a slipping off along an inclined surface is not possible.
The following is a detailed description of an embodiment of the invention with reference to the accompanying drawings.